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Slit lamp biomicroscopy

Eye Veterinary Clinic

Leominster

Herefordshire

UK

Christine Heinrich

slit lamp biomicroscope

• combination of a versatile light source with a

biomicroscope

• allows study of ocular structures and their

relationships in microscopic detail

• (photo documentation)

• developed by Gullstrand 1911

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basic components

• slit lamp illuminator

– precise and widely

adjustable light source

• biomicroscope

– provides a magnified

(6x-40x) 3D image

slit lamp biomicroscope

courtesy Animal

Health Trust

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components

illuminator and biomicroscope are

● parfocal

● i.e. focus on the same plane

● co-pivotal

● i.e swing on the same axis

● isocentric

● i.e. centre on the same placecourtesy of C

Martonyi

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courtesy of C

Martonyi

courtesy of C

Martonyi

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basic components

• slit lamp illuminator

– adjusts height and width of beam

– offers various filters (red-free, fluorescein

exciter, neutral density)

– allows horizontal displacement of the slit beam

from the vertical position

– allows vertical displacement of the beam from

the isocentric position (decentering)

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Health Trust

courtesy Animal

Health Trust

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basic components

• biomicroscope

– offers variable degrees of magnification

(x6 to x40)

– allows adjustment for observer refractive

errors and inter-pupillary distance

courtesy Animal

Health Trust

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photo slit lamp biomicroscopy

• several other features required

– beam splitter

– diffuse overall illuminator

– electronic flash

– camera body

– eye piece graticule

slit lamp biomicroscopy - principles

• isolation with illumination

• serial viewing of the eye with as many forms

of illumination as possible

courtesy of

C Martonyi

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Health Trust

courtesy Animal

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Health Trust

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forms of illumination

• direct illumination

– the examining light is directed on the structure

to be examined

• can be focal or diffuse

• retroillumination

– the structure of interest is illuminated by light

reflected from a posterior surface (iris or retina)

• can be direct or indirect

courtesy Animal

Health Trust

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slit lamp biomicroscopy - principles

• direct forms of illumination

– diffuse beam examination

• specular reflection

– focal examination

• optical sectioning

• distance estimation

• tangential exam

• Tyndall phenomenon

• indirect forms of

illumination

– direct retroillumination

• from the iris

• from the fundus

– indirect retroillumination

• from the iris

• from the fundus

direct illumination direct

retroillumination

indirect

retroilluminationindirect

retroillumination

with dark

background

courtesy Animal

Health Trust

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diffuse beam illumination

• advantages

– many changes best viewed with a broad beam

– allows a good overview

– especially important for adnexal and iris

examination

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Health Trust

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Health Trust

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diffuse beam illumination

• disadvantages

– fine detail (especially in transparent media) is lost

– viewing subtle changes requires:

• more selective illumination

• a decrease in the area of simultaneous examination

diffuse beam illumination

• specular reflection

– the reflected image of the light source itself

– brightness and intensity depend on the

reflectivity of the surface upon which it is seen

– permits assessment of integrity of the optical

surfaces (i.e. corneal epithelium, endothelium,

anterior and posterior lens surface)

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courtesy of C

Martonyi

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Normal dogZara, OD STT 5 Zara, OS STT 10

Zara, CKCS 3 y,

corneal ulceration

OD

Zara, CKCS 3 y,

mucoid discharge

OS

specular reflection of the endothelium

● surfaces of healthy

corneal cells are smooth

and highly reflective

● but borders are irregular

and highlighted by

absence of reflection

– HONEYCOMB

APPEARANCE OF

HEALTH ENDOTHELIUM

● pathology of cells results

in loss of reflection and

dark fill defects

● requirement: 25-40x

magnification!

http://www.opticianonline.net

direct focal illumination

• tangential illumination with a broad beam

– with the creation of distinct highlights and

shadows, the normally flat appearing surface of

the iris becomes vividly three-dimensional

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courtesy of C Martonyi

Direct illumination Direct illumination -

tangential

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Health Trust

courtesy Animal

Health Trust

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optical sectioning

• slit lamp biomicroscopes can produce an

optical section of the transparent tissues of

the anterior segment

• achieved by the projection of a narrow and

precisely delineated beam of light without

illumination of the adjacent areas

courtesy of C

Martonyi

courtesy of C

Martonyi

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Health Trust

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Martonyi

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Health Trust

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wide beam – watch trailing edge

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Health Trust

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courtesy Nils

Hakan-

Wallinson

courtesy Nils

Wallin –

Hakansson!

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Health Trust

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distance estimation

• with the help of a standard relationship

between eye, slit lamp and biomicroscope,

relative distances between surfaces can

easily be appreciated

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courtesy of C

Martonyi

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Health Trust

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Health Trust

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direct illumination

• pinpoint illumination (Tyndall’s phenomenon)

– ‘the rendering visible of of a transverse beam of light

through its being broken up by solid particles

suspended in liquid or gas’

– allows detection / quantitation of aqueous flare

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Narrow (short) beam, high intensity, wide angle

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Health Trust

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Health Trust

indirect forms of illumination

• especially useful for visualizing subtle

changes by enhancement of contrast

• slit beam may be de-centered from

optical axis

indirect forms of illumination

• proximal illumination

• sclerotic scatter

• retroillumination

– direct retroillumination from the iris

– indirect retroillumination from the iris

– retroillumination from the fundus

– iris transillumination

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indirect forms of illumination

• proximal illumination

– direction of a moderate slit beam adjacent to

an area of interest

– absorption / scattering of light around / behind

the abnormality enhancement of contrast

courtesy of C

Martonyi

courtesy of C

Martonyi

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courtesy Animal

Health Trust

courtesy Animal

Health Trust

indirect forms of illumination

• sclerotic scatter

– demonstration of subtle corneal abnormalities

– slit beam is decentred and directed at limbus

– light is absorbed by the sclera and scattered

throughout the cornea by total internal reflection

– abnormalities become evident through

reflection; the normal cornea is not visible

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courtesy of C

Martonyi

indirect forms of illumination

• retroillumination

– light reflected from iris or fundus can indirectly

illuminate subtle abnormalities anterior to these

surfaces

– the abnormalities appear dark against the bright

background created by the reflecting surface

retroillumination

• retroillumination from the fundus

– requires mydriasis and a narrow beam

– subtle lesions e.g. cataracts are readily appreciated

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courtesy of C

Martonyi

courtesy Animal

Health Trust

retroillumination

• retroillumination from the iris can be:

– direct: the iris immediately posterior to the

corneal interest is illuminated

– indirect: slit beam is further decentered - an

iris area away from the corneal lesion is

illuminated

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direct retroillumination

• retroillumination from

the iris can be:

– direct: the iris

immediately posterior

to the corneal interest

is illuminated

courtesy Animal

Health Trust

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indirect retroillumination

• retroillumination from

the iris can be:

– indirect: slit beam is

further decentered - an

iris area away from the

corneal lesion is

illuminated

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Health Trust

direct vs indirect retroillumination

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courtesy of C

Martonyi

indirect retro-illumination

direct retro-illumination

direct illumination

courtesy of C

Martonyi

courtesy Nils

Wallin –

Hakansson!

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Gelatt

Fig.10.1.23.

Fig.10.1.24.

retroillumination

• iris transillumination

– a narrow short slit is directed at the pupil

almost coaxial to the biomicroscope

– reflected light from the fundus will show iris

transillumination in areas of iris atrophy

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courtesy of C

Martonyi

type of opacity examined

• opacities in the clear optical media can

be characterized as

– obstructive

– refractive

– dispersive

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obstructive lesions

• block light on retroillumination (appear black

on bright background)

– for example

• active corneal blood vessels, corneal pigmentation

• blood clots in anterior chamber

• dense cataracts

• tissue masses

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Health Trust

translucent lesions

• allow passage of some light on

retroillumination

– detailed examination through lesion not

possible

for example

• keratic precipitates, corneal oedema, mild cataract,

fibrin, thin scars, cysts

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courtesy Animal

Health Trust

refractile lesions

• on retroillumination, light passes through

lesion but is refracted

– underlying tissues visible but distorted

– lesion takes on colour of background

for example

• nuclear sclerosis, incipient cataracts, distorted tear

film, corneal bullae

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further diagnostic procedures

• in gonioscopy

• for posterior segment examination using a

60 or 90 Diopter lens

• specialized instruments for pachymetry

and endothelioscopy

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OD

19/01/2010 OS

19/01/2010

OS

21/01/2010OS

26/01/2010

OCT ant segment

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Kowa SL 17 10×, 16× 1x1

0.1, 0.2,

0.8

5.0 and

12.0

circle

LED Cont Blue, white Video (via

iPhone

adapter)

0.79

Keeler PSL

classic

10×, 16× 1 × 1;

0.15,

0.5, 0.8,

1.6,

12.0

circle

LED Cont Red free,

blue, neutral

density,

clear

Video

(iPhone

adapter )

0.93

Hawkeye

(Dioptrix,

Toulouse,

France)

8×, 12.5×,

20×

1 × 1;

0.1, 0.2,

15.0

LED Cont Green (Red

free), Cobalt

blue

Photo and

Video (6

MPX

integrated

digital

camera)

1.5

(includin

g

camera)

Inbuilt

holder

for

fundus

exam

lenses

Reichert PSL

(Depew, NY)

10×, 16× 0.-11.0 LED Red free,

blue color

temperature

conversion

0.68

Kowa SL 15

●10x and 16x

mag

●blue and white

light

●4 lighting levels

●0.1, 0.2, 0.8

and full beam

●supports video

adapter

courtesy of

Barbara Braus

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courtesy of

Barbara Braus

courtesy of

Barbara Braus

Keeler PSL

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Hawkeye

●8x, 12x and

20x

magnification

●0.1, 0.2 and

full beam,

also 1.0 x1.0

spot for flare

●seamless

lighting level

adjustment

Hawkeye

Scan optic monocular slit lamp

●6x

magnification

●0.3 mm slit

●3.0 mm disc

●5.0 mm

square

●slit angle set

to 25% of the

corneal

surface

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Scan optic monocular slit lamp module for Welch

Allyn ophthalmoscope

●6x magnification

●0.4 mm slit

●3.0 mm disc

●5.0 mm square

●slit angle set to 35

degree angle of

the corneal surface